Weapon aim evaluation system

ABSTRACT

The system for evaluating the accuracy of aim of a missile firing weapon measures the line of aim of the weapon at the time of firing, measures the target flight path with an optical sensor and a radio ranging apparatus, and with a data processing unit calculates and compares a mean trajectory of a selected missile with either the actual or predicted target flight path indicating qualitatively and quantitively the error in aim.

United States Patent Michelsen Mar. 26, 1974 [541 WEAPON MM EVALUATIONSYSTEM FOREIGN PATENTS OR APPLICATIONS lflventori Paul MichelsenKensiflgton, 1.1171346 6/1968 Great Britain 35/25 [73] Assignee: RMCResearch Corporation,

Bethesda, Primary ExaminerStephen C. Bentley [22] Filed: July 3 1972Attorney, Agent, or Firm-Revere B. Gurley [21] Appl. No.: 268,632

[57] ABSTRACT 39/41 89/41 The system for evaluating the accuracy of aimof a l78/D 35, 343/6 TV, 343/12 M missile firing weapon measures theline of aim of the [51] Int. Cl. F4lg 3/26 weapon at the time of firing,measures the target flight Field Of Search 1 M 41 L, path with anoptical sensor and a radio ranging appa- 8 41 W; 173/1316. 1316- ratus,and with a data processing unit calculates and l l 343/6 12 MD comparesa mean trajectory of a selected missile with either the actual orpredicted target flight path indil References Clted cating qualitativelyand quantitively the error in aim.

UNITED STATES PATENTS 2,313,136 3/1943 Fischer 35/25 10 Clams 14 Drawmgfigures 1 l 1 l 1 [I 1 T.\/. 1 1 AV FRAME 1 A2111. l I l 1 l 1 ti o o TV[I 300 CAMERA zz z l VIDEO I CIRCUITS AZIMUTH ELECT gy z DATATRANSM'TTER RECEIVER TV ELEV. PROCESSING ELECT.

PHASE UNIT COMP POSITlQN DATA 600) PAIENIEDIIIARZB I974 3.798.795

MD I [If 9 START- START ANGLE A v ANGLE B STOP T P 246\ ROTATION MULT.MULT. ROTATION a COUNTER CONTROL --aA PULSES QI PULSES ,7 UNIT L E 248START STOP RESET 252 F a [0 I260 ELECTRONIC PRE-SET NUMBER Q E Q AZ'MUTH"TRANSFER DATA" CALIBRATION UNIT COMMAND FROM ADJUSTMENT l l I i DATAPROCESSOR AZIMUTH MEASUREMENT DATA (ANGLE C) TO DATA ENCODER PROCESSORROTATION PULSES FROM ENCODER MULT. a MC.

I66 I F76. 4 RESET PRESET NUMBER PULSE RESET ELEVATION CALIBRATIONCIRCUIT ADJUSTMENT |68 ELECT. COUNTING flso CIRCUITRY "TRANSFER DATA"COMMAND FROM I l 1 1 I DATA PROCESSOR Y J ELEVATION ANGLE DATA TO DATAPROCESSOR PATENTEBHARZS I974 SHEU 8 Bf 9 mum WEAPON AIM EVALUATIONSYSTEM This invention relates to the evaluation of operation of amissile-firing weapon, especially the accuracy of aim of a gun in aGunnery Training exercise.

Investigations have shown that the accuracy of antiaircraft weaponsvaries widely with different gunners. Both training and evaluation ofresults of gunners have been difficult and uncertain. Methods usingactual ammunition, as by firing at drones or at towed targets areexpensive, and the counting of hits can be accomplished only later andwith much additional effort. These systems convey no information of themisses or the pattern of gunfire, leaving the instructor or otherswithout knowledge of special problems of the individual gunner.

This invention is designed to be applied in a system under simulated oractual firing conditions. For training purposes, the weapon is operatedwith actual but ineffective ammunition, which is fired in a realisticmanner, but breaks up on leaving the gun, so that it is destroyed in afew yards. Thus, while providing all the effect on the gunner of actualfiring operation, it is possible to use an actual target, such as anaircraft, for training the gunner.

The primary object of the Weapon Aim Evaluation System of this inventionis to assess the accuracy of aim of the weapon and to register the errorin its angular position if a miss is indicated.

Other objects are to measure the angular position of the line-of-aim ofthe weapon at the time of firing, the angular position of theline-of-sight of the target aircraft, and the range distance of thetarget, all of these data to be input to a data processing unit forcalculations to provide the necessary information.

The hit-miss assessment of the gunnery operation, which is the basicoutput of this system, is effected by predicting the trajectory of theprojectile of each round fired and then determining if the predictedtrajectory would intersect the path of the target aircraft either asactually flown by the target or as predicted by, for example, a leastsquares analysis. The trajectory is determined from the ballistic datafor a mean projectile and measurements of the line-of-aim angles of theweapon at the time the round is fired. The trajectory is computed interms of elevation and azimuth angle of the line-of-aim and a rangemeasurement based on the position of the weapon in a common coordinatesystem (i.e., a spherical polar coordinate system).

The total Evaluation System is an integrated system in which the severalcomponents contribute to provide the Data Processing Unit (DPU) with thenecessary data and the DPU exhibits the results of the weapons operationfor evaluation. The system includes a ground operation with the gun andthe several ground components, and a target aircraft having other targetcomponents for cooperation with certain of the ground components.

The essential components of the system and their operation therein are:

l. The Weapon System with Angle Measurement.

The weapon itself, in the case illustrated an antiaircraft gun which hasassociated with it components for its line-of-aim measurement, in thiscase elevation angle measurement and azimuth angle measurement systems.The azimuth angle measurement system includes a Ground Point Locationelement so that the azimuth angle is measured in a coordinate systemoriented to the gun and yet is independent of changes in the gunposition. The data from these systems is supplied to the Data ProcessingUnit.

The object of the system used for elevation angle measurement is tomeasure the angular position relative to a zero position of an angularlymovable member at frequent small time intervals and to register suchangular measurement at any particular time.

The object of the system used for azimuth angle measurement is tomeasure the angular position of an angularly movable member relative toa fixed line or base line at frequent small time intervals, and toregister such angular measurement at any particular time. Thismeasurement is carried out with reference to a point external to themotion system of the movable member.

The elevation angle measurement and azimuth angle measurement systemsare complete angle measuring systems in themselves and have generalutility in measuring angular position. In both systems, electricalpulses are produced by a rapidly spinning body and input to a counter.The counting of pulses is controlled by the relative angular position ofthe gun to its mount in the elevation angle measurement and relative toa ground point position spaced from the gun in the azimuth anglemeasurement.

2. The Television Camera Direction System.

A television camera which follows the target provides for line-of-sightmeasurement of the target, by an elevation angle measurement and anazimuth angle measurement. The television camera has an electronicsystem which cooperates with a signal unit, a light on the target, andprovides an accurate measurement of the lineof-sight for data to besupplied to the DPU to be utilized in calculating the target position.

The object of the television camera direction system is to register thedirection of an object which produces an image on the sensitive surfaceof the camera. The source of the image is a light, and the coordinatesof the image on the surface with the directional angles of the cameratube are combined to provide an accurate measurement of the angles ofthe line-of-sight to the light.

3. The Distance Measurement System.

The distance or range measurement system, which measures the distance ofthe target constantly, and provides this data to the DPU. This systemincludes the transmitter, a transponder on the aircraft for transmittinga return signal, a receiver to receive the return signal, and phasemeasuring circuits to derive distance data for the DPU. The ground unit,or the transmitter, is mounted to move with the television camera, sothat the unit or its transmitter is directed toward the target. Thesetwo devices may be mounted on the same base for conjoint movement.

The object of this system is to measure a distant object by highfrequency radiations without ambiguity inherent in direct measurement byhigh frequency radiations. This system employs radiations spaced by alow frequency with a wave length comparable to the range of the system,utilizing the phase displacement of the low frequency to provide themeasurement.

THE DRAWINGS FIG. 1 is a diagrammatic view of the entire system.

FIG. 3 is another exploded view showing the apparatus of FIG. 2.

FIG. 4 is a schematic of the electronic circuit of the elevation anglemeasurement system, which is connected to the apparatus of FIGS. 2 and3.

FIG. 5 is a diagrammatic view of the azimuth measurement system for thegun.

FIG. 6 is a diagram illustrating how the angles are measured by thesystem of FIG. 5.

FIG. 7 is a diagrammatic view showing the operation of the system ofFIG. 5.

FIG. 8 is a perspective'view of the unit on the gun mount which moveswith the gun about a vertical angle.

FIG. 9 is a vertical axial section of the unit of FIG. 8.

FIG. 10 shows the electronic circuitry for providing data of the valueof the azimuth angle, from the system of FIGS. 5 to 9.

FIG. 11 shows the electronic circuit which provides the values of thecoordinates of the image on the frame of the television camera.

FIGS. 12A and 12B are a composite block diagram of the ground radioapparatus.

FIG. 13 is a block diagram of the radio apparatus on the target.

SYSTEM OPERATION The missile-firing weapon, or anti-aircraft gun 10, isplaced at a point x y Z in a common coordinate system. The elevationangle measurement 100 provides the data of the elevation angle of thegun as it is moved by the gunner, and the azimuth angle measurementsystem 200 provides the data for the azimuth angle. A ground pointlocation unit 210 at a point X y,, z, in the common coordinate system isused as a reference position for measurement system 200 of the azimuthangle. The elevation and angle measurement systems transmit pulses whichrepresent the values of the angles to electronic averaging andmultiplier units.

The TV camera 300 at position x2, y Z2 in the common coordinate systemmay be manually moved to follow the target or could be movedautomatically. In addition to devices for measurement of the elevationand azimuth angles of its line-of-sight, the camera is provided with anelectronic scanning measuring system for registering the position of asignal light 502 carried by the aircraft target 500. The elevation andazimuth angle measuring systems and the electronic video signalmeasuring system transmit data of the values of these measurements tothe Data Processing Unit (DPU) 600. With the data from these systems,the DPU can make an accurate calculation of the position of the target.

The range or distance measurement system 400, with the ground unittransmitter at x y 2 also includes the transponder 422 on the aircrafttarget 500, which relays the return signals to the ground receiver at xy.,, 2 This system, transmitting in high radio frequencies, uses anarrow band and measures the distance unambiguously with standardcircuitry to the necessary accuracy for this purpose.

Operation of the firing mechanism of weapon 10 activates the DPU throughlead 20 initiating the calculations from the data input of the weapon,TV camera,

and range measurement systems. The DPU calculates the path of aconventional projectile and compares it to the flight of the targetaircraft either as actually flown by the target or as predicted by, forexample, a least squares curve fitting calculation. The DPU may thenexhibit at 30 the score of hit or miss as well as the errors inelevation and aximuth angles.

ELEVATION ANGLE MEASUREMENT The apparatus for measuring the angle ofelevation of the gun comprises a casing 102, 103 on the gun supportingstructure and an arm 106 fixed to and angularly movable with the gun.The casing, formed in two parts, 102 and 103, encloses a motor 108,having its axis aligned with the axis 110 of the trunnions of the gunbut not mechanically connected so that its shaft revolves about the sameaxis. A plate 112 on the shaft of the motor carries a supporting member114, which is fastened to the rotating disk 116. The supporting member114 is formed with a pocket or is cut away at 118 to receive a lightdisplacing and reflecting element in a casing 120 fixed to a disk 116.

The disk 1 16 operates to produce electrical pulses by a light 112 andphotocell 124 mounted adjacent its periphery, the disk being formed withapertures 126 or light deflecting elements about its periphery. Thephotocell is energized at regular intervals as the disk rotates, therebyproducing electrical pulses from the photocell 124.

The disk 116 is also formed with a narrow, radial slit or aperture 128,opposite the casing 102. This casing carries mirrors to deflect lightpassing through the aperture 128 and a lens 129 aligned with the axis ofrotation 110, to direct the light on to a photocell 130 positioned onthe axis.

The casing carries a light source 132 in a light casing 134 providedwith a mirror 136 to reflect the light on to the disk 116 and throughthe aperture 128 as it passes the casing. The casing may carry a lenssystem 138 which may include a cylindrical lens to form a narrow beam oflight.

Arm 106 is formed as a second, elongated light casing secured to thegun, as through an adapter 142, to move with the gun and projects intothe casing 102. This casing 106 carries a light 144 at its outer end,the light from which passes through a lens system 146 which, like lenssystem 138, has a cylindrical lens.

The other end of casing 106 extending into casing 102 carries a mirrow148 opposite the path of the aperture 128. The casing 102 may beprovided with a flexible closure where the light casing 106 passes intoit to avoid light from outside the casing 102, 103.

The disk is driven rapidly by motor 108 and produces rapid, successivepulses from light 122 and photocell 124, which are connected to theelectronic multiplier and averaging circuit 150 (FIG. 4).

When aperture 128 in disk 116 rotates past the light beam from fixedlight 132, the photocell 130 produces a start pulse which is transmittedto the counting circuit (FIG. 4) to the counter to start registering ofthe count. This counter 160 receives the pulses produced by the disk 116and photocell 124 through the multiplier and averaging circuit 162.These pulses are registered successively until the slit in rotating disk116 reaches the light beam from the angularly movable light 144 andcasing 106, producing a pulse from photocell H30 which is transmitted tocounter 160 to discontinue the count.

An elevation angle calibration adjustment circuit 166 presets thenumber'in the counter to set the counter for a zero horizontal angle.The start and stop pulses pass through a reset pulse circuit 168 whichis connected to the calibration adjustment circuit so that the counterwill be properly set at the beginning of each count.

AZIMUTH ANGLE MEASUREMENT The measurement of the position of theangularly movable gun mount about a vertical axis is not easily measuredin the same way as the elevation angle, because the weapon shifts itsposition relative to the ground due to recoil. The system used byapplicant provides a ground point location unit 210 spaced from the gunmount (FIG. 5) so that the data of angular position relative to thefixed ground point location may be transmitted to the computer and usedto calculate the azimuth angle relative to a fixed base line. Thismethod, illustrated in FIG. 6, involves measuring the angle A of the gunrelative to a line between measuring units on the angularly movable gunmount and the ground point location unit, the angle B between this lineand a fixed base line having zero direction, from which the angle C ofthe gun with respect to the zero base line may be calculated, i.e.,C=360(A+B).

The unit 220 movable with the gun is shown in FIGS. 7 and 8. This unitproduces pulses which are used to measure angular position incooperation with a light and photocell on the ground point locationunit.

The counting pulses for measuring angle A are produced by a disk 222having peripheral apertures which are in the path of light from lightsource 224 to photocell 226. A motor 223 drives disk 222 about avertical axis. These pulses are fed to a counter circuit under controlof start-stop pulses.

A light 228 fixed on the unit 220 in a light tube 229 passes through alens system 230 having a cylindrical lens to form a narrow beam and isreflected by mirror 2311 on to disk 222, passing through an aperture inthe disk to energize photocell 232. The energization of this photocellproduces a start pulse for the counting circu|t.

A mirror 233 mounted on the shaft of the motor above the disk cooperateswith a light 234 and photocell 235 on the ground point location unit toproduce a stop pulse to the counter circuit. Since the mirror rotateswith the disk, the position of the mirror relative to the ground pointat the time the photocell is energized will depend on its angle ofrotation from the fixed or zero position which formed the start pulse,and the count of the pulses will form a measure of the angle A.

To measure angle B, the ground point location unit carries a disk 240 toproduce counting pulses. The ground unit also employs a light 241, amirror 242 rotatable with the disk and a photocell which receives lightreflected by the mirror to provide a fixed reference position. The unit220 on the gun mount also carries a photocell 244 axially aligned withthe axis of the disk and mirror, which receives light from mirror 242,to provide a stop pulse to the counting circuit, the counting pulsesbetween the start and stop pulses representing the measure of angle B.

The counting circuit shown in FIG. 10 includes a multiplier andaveraging circuit 246 for pulses from angle A measuring system andanother circuit 248 for pulses from angle B measuring system. The startand stop pulses for angle A measurement are fed into the counter controlunit 252 at the left and those for angle B measurement at the right. Thecontrol unit 252 under command of the Data Processing Unit may transferthe data from the control unit to the counting unit 260 which is alsocontrolled by the control unit. A calibration adjustment 262 providesfor presetting the counting unit to a zero or reference setting.

TELEVISION CAMERA TARGET TRACKER The television camera is used to trackthe target and with associated elements and electronics provide ameasure of the angular position of the target. The elevation and azimuthangles are used to register the lineof-sight of the camera and the dataof these angles and the location of the target within the camerasfield-ofview is fed to an electronic unit for the determination of theexact angular position of the target.

In the present system the target aircraft carries a signal light whichgives substantially a point image on the TV frame. The TV camerasubtends a substantial angle while the image of the target may occupyonly a small spot somewhere on the frame of the TV camera. There fore,the line-of-sight will, in general, give only a coarse and unreliablemeasure of the angular location of the target. A more accurate measureof the angular location of the target is necessary for accurateevaluation of the gunnery operation. For this purpose, the position ofthe image is located on the frame in the camera, and this position isrelated to the direction of the camera axis or line-of-sight. This lightmay be infrared, to avoid confusion of the gunner, and can be obtainedby filtering broad band light to shut out visible light. The position ofthe point light on the TV frame is measured by the scanning trace of theTV camera, and the data from the trace is then inputted to theelectronic unit to modify the camera direction data and give the trueline-ofsight of the target.

The television camera 300 is mounted for movement in all directions,i.e., the elevation angle and azimuth angle, being measured by anglemeasuring apparatus similar to the elevation angle measuring device onthe gun. The camera is moved to keep the target airplane 500 in itsline-of-sight, the light 502 on the plane forming an image on thesensitive surface 310 of the TV camera. In general, the image on thetelevision frame will be spaced from the center axis, or the boresight,of the camera, and the position is located in the frame to give anaccurate measure of the image location with re spect to the boresight.The television frame under American standards is scanned 525 lines perframe 30 times a second to produce a picture signal but other scanningpatterns may be used. The position of the image of the light in theframe can be measured by registering the line which intersects the imageand the length of the line from the start of the line to the position ofthe image.

The size of the image of the signal light on the image surface of the TVtube should be at least as large as the width of two or three lines (oron the order of 3/l,000 of an inch for a TV camera tube with a k X inchactive area. With a small light that is necessary on the target, asharply focused image may produce almost a true point which is not largeenough to insure registering on the image surface with the scanningtrace. The spot of the light may be made larger by displacing the imagesurface to either side of the in-focus plane of the lens, i.e., bydisplacing from the in-focus point of the lens, to increase the pointimage on the image surface to spot sufficiently large for registering bythe scanning trace,

Recognition of the light signal on the tubes sensitive surface is madeon the basis of the highest level of the video signal during a scan ofthe electron beam. The circuit for recognizing this peak level andregistering its position is shown in FIG. 11. For this purpose, thelight must be intense enough to form an image of greater brightness thanits background and, as described, large enough to be intersected byseveral lines. Infrared light has been found to be preferable as it isinvisible to the gunner and penetrates moisture or haze better thanlight in other portions of the spectrum.

The start of the scan initiates the counter 320, which then counts theline traces until the end of the scan, when it is reset. The videosignal has an input to a peak reader circuit 330 which, on receiving apeak video signal higher than preceding signals from the camera, enablesgate 322 to pass the count from counter 320 to a register 324 whichthereby registers the number of the line in which that peak occurred.

At the start of the scan, the peak reader will cause the first linenumber to be transferred as any video signal of a line trace signal willbe greater than zero. A video signal of a higher level than that of thefirst line will then cause the transfer of the number of that line toregister 324 replacing the previous number. No transfer signal occurswhen the signal level of a lines video signal is not higher than theprevious high level, so that at the end of the scan, the number of theline with the highest signal level, or greatest light intensity, isstored in register 324, to give one coordinate of the light image on theframe of the TV tube.

The other coordinate is obtained by measuring the point on the line thatthe peak signal occurred. This measure is made in a counter 340 byregistering a series of pulses from the start of the line; the number ofpulses, N, being determined by the resolution required.

In the example shown, a crystal controlled oscillator 342 and the pulsegenerator 344 operate at a frequency of 3,9l625 MHZ to transmit 3.91625X 10 PPS to the countdown circuit 340, which reduces the pulse rate bydividing by 256 to give 15.75 X 10 PPS which provides the master pulseto the TV camera raster generator. These pulses also supply thecountdown circuit 320.

The gate 348 passes the count in counter 340 to the register 350 undercontrol of a signal from the peak reader circuit in the same manner asfor the line counter, so that the register contains the number of pulsesfrom the beginning of a line, which indicate the position on the linethat a peak level intensity occurs.

As the image of the light can be wider than the equivalency of one countdistance along a line, the signal from the peak reader to the gatecauses, first, the count in the countdown circuitry unit that exists atthe beginning of the new high peak signal to be transferred to theregister counter 350 via a gate 348, then increases the count in theregister one count for each two counts inputted to the countdowncircuitry unit through division circuit 352 and gate 354. After thepassage of the high, the register 350 will have a count which is relatedto the center of the high signal, and higher ac curacy results.

The operation of the gun at the proper time will cause the dataprocessing unit to read out the registers 324 and 350 into the DPU,giving the counts corresponding to the coordinates of the peak levelsignal on the image surface of the television camera frame 310, undercontrol of a transfer data pulse from the DPU. The DPU then calculatesthe true line-of-sight of the light beacon on the target,

Following the scan of each frame 310 of the television camera, an endscan signal from the camera resets the counter 320 and registers 324 and350 for the next scan.

RANGE MEASUREMENT SYSTEM The range measurement system used is of generalapplication for measuring the distance between two points. The basis formeasurement is the phase displacement of a long wave radiation signalwhich has a length as great as the distance to be traversed from onepoint to the other and return, so that the ambiguity of a phasedisplacement of more than 360 is avoided. By this invention, the sameresult is obtained by transmit ting two continuous wave radiationsf, andf differing by the low frequency f (f, =fi,f,) and subsequentlymeasuring the phase displacement of the low frequency f,, at thereceiver. The two transmission frequencies may be produced by adding thelow frequency f to a higher frequency f,,, the two frequencies f, and f+f then being combined with a high frequency f The two frequgncies f1 fz(fl f;4+fc and f2 f4 fC fR l fR) may then be transmitted as twocontinuous wave radiations.

The transmitting apparatus A shown in FIG. 12 utilizes a crystaloscillator 40] with output f (fi Nf connected to a pulse generator 402to produce pulses at f rate. These pulses then go to a countdown circuit403 with output of pulses [f,,/(N/2)]. These are fed to a flipflopcircuit 404, producing square waves of f frequency, which are formedinto sine waves by filter 405 and input to converter 406. The output ofcrystal oscillator 407 frequency f combines with f in converter 406(f,;=f, +fn) and is filtered at 408, which passes only frequency f Acrystal oscillator 410 with output f connects to converter 412, whichalso receives inputsf from oscillator 407 and f from filter 408 toproduce the transmitting frequencies f, and f (f,=f +f Qf =f +f +f Theband pass filter 414 passes the high frequency band only slightly widerthanf i.e.,f and f which are amplified by amplifier 416 and poweramplifier 418, to be radiated by antenna 420.

The transmitted high frequency radiations f f are received by thetransponder 422, consisting of a receiver and transmitter, at a distantpoint, in this case on the target 500. These signals are amplified inamplifier 424, combined in converter 425 with outputf of crystalconstrolled oscillator 426 and passed through filter 428 to amplifier430. After amplification in linear amplifier 432, the high frequencysignals f f, (f +f jI,=f +f are transmitted by antenna 434 as continuouswave radiations differing by low frequency f The radiations f f, fromthe transponder are received by antenna 440 of the receiver B, in thiscase associated with transmitter A, and after amplification in amplifier442, combine with output f,,- of crystal controlled oscillator 444 inconverter 446 and pass through filter 448 as frequencies f and fdiffering by frequency f,;. The phase-lock loop circuits 450, 452 eachrespond to one of the frequencies f and f which are then combined inmultiplier circuit 454 to form the difference frequency f the filter 455passing only f This f the difference frequency of the transmissions fromthe first point to the second point and return, has been displaced inphase in proportion to this distance. This f is now compared with thedifference frequency f from f f in the transmitters in the phasecomparison circuit 456. V

These latter f pulses are derived from pulses produced by the pulsegenerator 402, at the f rate, which pass to gate 460 directly, and alsoto the gate through inverter 462. This gate may pass the pulses atf rateto the countdown circuit 464, where the output from the gate is dividedby N/Z to give pulses to the flipflop circuit 466 which has a squarewave output at the f rate and fed to phase comparison circuit 456.

The square wave from the flipflop 466 at the f rate, derived from thesource frequency, is input to the phase comparison circuit 456 with thesine wave signal f,. which is the round trip signal from the distantpoint. The output of the phase comparison circuit 456 and its averagingcircuit 458 varies in amplitude and polarity according to the phasedifference between the two signals, and is positive or negative when thephase of one signal is ahead or behind the phase of the other. Thisvoltage is fed to the gate circuit 460, which receives positive pulsesat the f rate directly from pulse generator 402 and also from theinverter 462, the negative pulses from the pulse generator producing thepositive pulses from the inverter intermediate in time with respect tothe direct pulses.

With no voltage applied to the gate 460 from the phase comparison andaveraging circuits, the gate passes positive pulses at the 1",, rate tothe countdown circuit 464. A no voltage condition for the phasecomparison circuit occurs when no phase difference exists between theinput signals.

A positive voltage from the phase comparison circuit 456 to the gatecircuit 460 will cause additional pulses to be supplied to the countdowncircuit from the inverter 462, thereby advancing the square wave in timeand therefore its phase. These additional pulses from gate 460 willcause the counter 470 to step ahead. When the voltage from the phasecomparison and averaging circuits is negative, the gate will stop ornegate the pulses arriving at the gate directly from the pulse generatorand the countdown action will be retarded as long as the negativevoltage exists. The stability of the circuit is assured by inputting asignal from the flipflop 466 to the gate 460, so that only one pulse canbe added or negated in one f cycle.

In operation a difference in phase of the two signals results in anoutput of the phase comparison circuit which causes a shift in thesquare wave so as to achieve alignment of the phase of the square wavewith that of the round trip signal. As the phase of the round tripsignal received varies due to change in distance of a moving point, thecircuit responds to follow the change.

To obtain the range data in digital form for the data processor, thepulses from the gate to the countdown circuit are also inputted to thebinary counter 470 of N stages. This counter will therefore be cycledthrough a full count for each cycle of the range measurement frequency.The output of the binary counter then passes through calibrationadjustment circuit component 472 to a binary register 474. The leadingedge of the f square wave at the output of flipflop unit 404 initiatesthe transfer of the contents of Binary Register 474, which at thatmoment will be a binary equivalent of the measured range, to the DPU.

The calibration adjustment component 472 provides for a calibrated rangesetting for the system. The setting is required since the phase of therange measuring frequency in its round trip is affected by thecomponents of the system and the several circuits, including wiring andcables. Once the system is constructed and installed, these phase shiftsare fixed.

The calibration adjustment component 472 may be set by comparing with aknown distance of the aircraft on which the system is installed and theground unit, then manually setting the calibration adjustment control togive a range data reading of the known distance. This setting may bemade at the airport with the aircraft unit on the ground a measureddistance from the ground unit. This procedure should be followed whenany changes take place in the aircraft or in the installation of theunit.

For day-to-day operations, the ground unit may be checked using anaircraft unit at a known distance to ascertain if the system isproviding correct data. As this unit may differ in its phase shiftcharacteristics from the one installed on the aircraft, an initialmeasure of this difference must be obtained by comparing the setting forthe test unit and for the aircraft installation.

This range measurement system is unusually stable, since it is lesssubject to external conditions than many other types of systems. A majorinfluence on circuit phase constancy is the temperature of circuitelements as, for example, capacitors which may change in value withtemperature, and consequently the characteristics ofa circuit and itsphase effect. The present system obviates or reduces temperature effectssufficiently that ordinary circuit design and construction techniquesmay be employed. This effect is the result of using two closely spacedsignals, as f and f or f and f which pass through the same circuitelements and circuits. External conditions, such as temperature change,will affect both signals to substantially the same extent, so that therelative phase differences of the two signals will be substantiallyconstant.

Operation of this system with the narrow band necessary in the very highfrequency range results in economies of standard circuitry and lowpower. Interference in this range, as well as noise effects, are less ofa problem, and allocations are more likely to be available. The problemsand circuitry inherent in modulating the carrier frequencies are alsoavoided.

This distance measurement system will have a usable range comparable tothe wavelength corresponding to the difference frequency f For example,the difference or range measuring frequency of 7.5 KHZ gives anunambiguous measurement of range up to 18 kilometers. This range issatisfactory for the purposes of the Weapon Aim Evaluation System. Therange measurement accuracy is a function of an incremental unit of thewavelength of frequency f however, if a greater accuracy is required, avenier effect may be provided ill by the phase measurement of one of thehigh frequencies f or f with a correspondingly more sophisticatedcircuitry for producing a fine, unambiguous measurement at the higherfrequency.

The two transmitted continuous wave radiations in this system aretransmitted as two separate signals. The same effect could be producedby other means, for example, by two side bands of a single carrier,spaced by the difference frequency f (7.5 KHZ in the example), and thecarrier frequency could be eliminated at the transmitter.

SUMMARY In the use of this system for training, the DPU cornpares theline of aim selected by the weapon operator and ballistic informationconstants known about selected missiles with the possibly evasive pathtaken by the target aircraft as measured by the television camera andradio ranging apparatus and provides an accurate measure of misses aswell as a registration of hits. The exhibition of the errors in bothangles of elevation and azimuth will show quantitively the direction anddegree of error and provide a basis for correction of the aim of anindividual weapon operator.

1 claim:

1. In a system which comprises a weapon to be aimed to direct a missileat a target, a television camera which registers a signal on the imagesurface when directed toward said target, radio transmitting andreceiving apparatus transmitting radiation toward and from said target,a data processing unit (DPU), and a register to exhibit the differencebetween the correct line of aim and the line of aim of said weapon, themethod of exhibiting the accuracy of the aim of said weapon comprisingl. Registering in said DPU data denoting the positions of saidtelevision camera, and said transmitter and receiver apparatus relativeto said weapon,

2. Measuring the angular position of the line of aim of said weapon andtransmitting the data denoting said position to said DPU,

3. Measuring the angular position of the line of sight of said targetregistered on the image surface of said television camera andtransmitting the TV data digitally to said DPU,

4. Measuring the distance to the target by transmitting to said targetdistance measuring continuous wave radiations and receiving returncontinuous wave radiations initiated at the target by said transmittedradiations, and measuring the distance by the effect of the distance onsaid radiations, and transmitting the distance data digitally to saidDPU,

5. Actuating said DPU by the action of firing said weapon to derive fromsaid TV data and said distance data a measurement of the correct line ofaim of said weapon to direct a missile to said target,

6. Comparing the line of aim of said weapon with the correct line of aimand exhibiting the difference between the measurements of the correctline of aim and the measurement of the line of aim of said weapon togive a quantitative indication of the accuracy of the weapon operation.

2. in a system which comprises a weapon to be aimed paratus transmittingradiation toward and from said target, a data processing unit (DPU), anda register to exhibit the difference between the correct line of aim andthe line of aim of said weapon, the method of exhibiting the accuracy ofthe aim of said weapon comprising 1. Registering in said DPU datadenoting the positions of said television camera and of saidtransmitting and receiving apparatus relative to said weapon,

2. Measuring angles of elevation and azimuth of the line of aim of saidweapon and transmitting the data denoting said position digitally tosaid DPU,

3. Measuring the angles 0f elevation and azimuth of the line of sight ofsaid television camera and transmitting the data digitally to said DPU,

4. Measuring the distance to the target by transmitting to the targettwo high frequency continuous wave radiations differing by a lowfrequency radiation having a wave length at least as great as thedistance to and from said target, and returning two high frequencycontinuous wave radiations differing by the same low frequency to bereceived by the receiving apparatus, and comparing the differencefrequencies of said transmitted and received radiations to ascertain thephase displacement of the transmitted frequencies resulting from thedistance traversed, and transmitting the data of said phase displacementand distance digitally to said DPU,

5. Actuating said DPU at the firing of said weapon to derive from saidtelevision camera data and said distance data the correct line of aim ofsaid weapon to direct a missile to said target, and

6. Comparing the line of aim of said weapon with the correct line of aimand exhibiting the difference to provide an indication of the accuracyof the operation of said weapon.

3. In a system which comprises a weapon to be aimed to direct a missileat a target which has a light source, a television camera whichregisters a signal on the image surface when directed along a line ofsight toward said target, radio transmitting and receiving apparatus fortransmitting radiation toward and from said target, a data processingunit (DPU), and a register to exhibit the difference between the correctline of aim and the line of aim of said weapon, the method of exhibitingthe accuracy of the aim of said weapon comprising l. Registering in saidDPU data denoting the positions of said television camera and saidtransmitter and receiver apparatus relative to said weapon,

2. Measuring the angular position of the line of aim of said weapon andtransmitting said data digitally to said DPU,

3. Measuring the angular position of the line of sight of saidtelevision camera and transmitting the data digitally to said DPU (a)Sensing the position of the image of said light source on the framescanned on the TV image surface and transmitting to said DPU dataderived from said position to give the accurate line of sight of saidlight source on said target,

4. Measuring the distance to the target by transmitting to said targettwo high frequency continuous wave radiations, the difference betweenwhich is a 'low frequency having a wave length at least as great as thetotal distance traveled by the radiations, and transmitting from thetarget radiation initiated by said first radiation comprising two highfrequency continuous wave radiations differing by the same low frequencyas said original transmitted radiations, comparing the differencefrequency of the transmitted radiations with the difference frequency ofthe received radiations to determine the phase displacement resultingfrom the distance traveled, and transmitting to said DPU data denotingsaid phase displacement and distance of the target, and

5. Actuating said DPU upon firing the weapon to derive from said line ofsight data and said distance data the correct line of aim of said weaponto direct i a missile to the target and comparing the line of aim ofsaid weapon with the correct line of aim, and exhibiting the differenceto give an indication of the accuracy of the operation of said weapon.

4. In a system as in claim ll, the method claimed therein whichcomprises exhibiting the differences between the angles of elevation andazimuth, respectively, of the correct line of aim and the line of aim ofthe weapon at the time of firing, so that the quantitative valuesindicate the inaccuracy in each angle of the line of aim of the weapon.

5. In a system as in claim 3, the method therein claimed which comprisestransmitting from said target two high frequency radiations offrequencies differing from the frequencies of said radiationstransmitted to said target.

6. In a system for evaluating the accuracy of the aim of amissile-firing weapon at a target, said system comprising measuringapparatus connected to said weapon to measure the angular position ofthe weapon at the time of firing and electronic means to produce digitalvalues of said angular position, a television camera mounted for angularmovement to follow the target with its image on the TV image surface,and means to measure the direction of the line of sight of said targetincluding means to measure the angular position of the TV camera andfurther means to measure the position of the target image on the TVimage surface, range measuring apparatus comprising first radioapparatus to transmit and receive two high frequency radiations to andfrom said target which differ by a low frequency having a wavelength atleast as great as the distance to and from said target, radio apparatusat said target receiving the transmitted high frequency radiations andtransmitting back two high frequency radiations differing by the samelow frequency as said original radiations, first receiving apparatusreceiving said return radiations, electronic circuit means comparing thelow frequency difference of the received radiations with the lowfrequency differences of the original transmitted radiations to measurethe phase difference of the re ceived radiation and thereby the distancetraveled by the original and return radiations, a data processing unit(DPU), electronic means to transmit data digitally to said DPU from themeasurements of the angular position of said weapon, the measurements ofthe angular position of said television camera and the position of saidimage on said image surface, and data from said range measuringapparatus, means to activate said DPU operated by the firing mechanismof said weapon, and exhibition means controlled by said DPU to exhibitthe quantitative difference between the correct line of aim and the lineof aim of said weapon.

7. In a system as claimed in claim 6, in which said radio apparatus atsaid target transmits high frequency radiations which differ infrequency from the high frequency radiations transmitted by said firstradio apparatus.

8. In a system as claimed in claim 6, in which a light source ispositioned on said target, and forms an image on the image surface ofsaid television camera.

9. In a system as claimed in claim 6, in which the measuring apparatusto measure the elevation angle of said weapon is carried by the weaponsupporting structure, and the azimuth angle measuring apparatus includesa ground location point spaced from said supporting structure to providea measurement of the azimuth angle by reference to a fixed groundposition,

10. In a system according to claim 9, in which said DPU actuates saidexhibition means to exhibit the differences in the values of the anglesof elevation and azimuth, respectively, between the correct line of aimand the line of aim of said weapon.

1. Registering in said DPU data denoting the positions of saidtelevision camera, and said transmitter and receiver apparatus relativeto said weapon,
 1. In a system which comprises a weapon to be aimed todirect a missile at a target, a television camera which registers asignal on the image surface when directed toward said target, radiotransmitting and receiving apparatus transmitting radiation toward andfrom said target, a data processing unit (DPU), and a register toexhibit the difference between the correct line of aim and the line ofaim of said weapon, the method of exhibiting the accuracy of the aim ofsaid weapon comprising
 2. Measuring the angular position of the line ofaim of said weapon and transmitting the data denoting said position tosaid DPU,
 2. Measuring the angular position of the line of aim of saidweapon and transmitting the data denoting said position to said DPU, 2.In a system which comprises a weapon to be aimed to direct a missile toa target; a television camera which registers a signal on the imagesurface when directed toward said target, radio transmitting andreceiving apparatus transmitting radiation toward and from said target,a data processing unit (DPU), and a register to exhibit the differencebetween the correct line of aim and the line of aim of said weapon, themethod of exhibiting the accuracy of the aim of said weapon comprising2. Measuring angles of elevation and azimuth of the line of aim of saidweapon and transmitting the data denoting said position digitally tosaid DPU,
 2. Measuring the angular position of the line of aim of saidweapon and transmitting said data digitally to said DPU,
 3. In a systemwhich comprises a weapon to be aimed to direct a missile at a targetwhich has a light source, a television camera which registers a signalon the image surface when directed along a line of sight toward saidtarget, radio transmitting and receiving apparatus for transmittingradiation toward and from said target, a data processing unit (DPU), anda register to exhibit the difference between the correct line of aim andthe line of aim of said weapon, the method of exhibiting the accuracy ofthe aim of said weapon comprising
 3. Measuring the angular position ofthe line of sight of said television camera and transmitting the datadigitally to said DPU (a) Sensing the position of the image of saidlight source on the frame scanned on the TV image surface andtransmitting to said DPU data derived from said position to give theaccurate line of sight of said light source on said target,
 3. Measuringthe angular position of the line of sight of said target registered onthe image surface of said television camera and transmitting the TV datadigitally to said DPU,
 3. Measuring the angles of elevation and azimuthof the line of sight of said television camera and transmitting the datadigitally to said DPU,
 3. Measuring the angular position of the line ofsight of said target registered on the image surface of said televisioncamera and transmitting the TV data digitally to said DPU,
 4. Measuringthe distance to the target by transmitting to the target two highfrequency continuous wave radiations differing by a low frequencyradiation having a wave length at least as great as the distance to andfrom said target, and returning two high frequency continuous waveradiations differing by the same low frequency to be received by thereceiving apparatus, and comparing the difference frequencies of saidtransmitted and received radiations to ascertain the phase displacementof the transmitted frequencies resulting from the distance traversed,and transmitting the data of said phase displacement and distancedigitally to said DPU,
 4. Measuring the distance to the target bytransmitting to said target distance measuring continuous waveradiations and receiving return continuous wave radiations initiated atthe target by said transmitted radiations, and measuring the distance bythe effect of the distance on said radiations, and transmitting thedistance data digitally to said DPU,
 4. Measuring the distance to thetarget by transmitting to said target two high frequency continuous waveradiations, the difference between which is a low frequency having awave length at least as great as the total distance traveled by theradiations, and transmitting from the target radiation initiated by saidfirst radiation comprising two high frequency continuous wave radiationsdiffering by the same low frequency as said original transmittedradiations, comparing the difference frequency of the transmittedradiations with the difference frequency of the received radiations todetermine the phase displacement resulting from the distance traveled,and transmitting to said DPU data denoting said phase displacement anddistance of the target, and
 4. Measuring the distance to the target bytransmitting to said target distance measuring continuous waveradiations and receiving return continuous wave radiations initiated atthe target by said transmitted radiations, and measuring the distance bythe effect of the distance on said radiations, and transmitting thedistance data digitally to said DPU,
 4. In a system as in claim 1, themethod claimed therein which comprises exhibiting the differencesbetween the angles of elevation and azimuth, respectively, of thecorrect line of aim and the line of aim of the weapon at the time offiring, so that the quantitative values indicate the inaccuracy in eachangle of the line of aim of the weapon.
 5. Actuating said DPU uponfiring the weapon to derive from said line of sight data and saiddistance data the correct line of aim of said weapon to direct a missileto the target and comparing the line of aim of said weapon with thecorrect line of aim, and exhibiting the difference to give an indicationof the accuracy of the operation of said weapon.
 5. In a system as inclaim 3, the method therein claimed which comprises transmitting fromsaid target two high frequency radiations of frequencies differing fromthe frequencies of said rAdiations transmitted to said target. 5.Actuating said DPU at the firing of said weapon to derive from saidtelevision camera data and said distance data the correct line of aim ofsaid weapon to direct a missile to said target, and
 5. Actuating saidDPU by the action of firing said weapon to derive from said TV data andsaid distance data a measurement of the correct line of aim of saidweapon to direct a missile to said target,
 5. Actuating said DPU by theaction of firing said weapon to derive from said TV data and saiddistance data a measurement of the correct line of aim of said weapon todirect a missile to said target,
 6. Comparing the line of aim of saidweapon with the correct line of aim and exhibiting the difference toprovide an indication of the accuracy of the operation of said weapon.6. Comparing the line of aim of said weapon with the correct line of aimand exhibiting the difference between the measurements of the correctline of aim and the measurement of the line of aim of said weapon togive a quantitative indication of the accuracy of the weapon operation.6. Comparing the line of aim of said weapon with the correct line of aimand exhibiting the difference between the measurements of the correctline of aim and the measurement of the line of aim of said weapon togive a quantitative indication of the accuracy of the weapon operation.6. In a system for evaluating the accuracy of the aim of amissile-firing weapon at a target, said system comprising measuringapparatus connected to said weapon to measure the angular position ofthe weapon at the time of firing and electronic means to produce digitalvalues of said angular position, a television camera mounted for angularmovement to follow the target with its image on the TV image surface,and means to measure the direction of the line of sight of said targetincluding means to measure the angular position of the TV camera andfurther means to measure the position of the target image on the TVimage surface, range measuring apparatus comprising first radioapparatus to transmit and receive two high frequency radiations to andfrom said target which differ by a low frequency having a wavelength atleast as great as the distance to and from said target, radio apparatusat said target receiving the transmitted high frequency radiations andtransmitting back two high frequency radiations differing by the samelow frequency as said original radiations, first receiving apparatusreceiving said return radiations, electronic circuit means comparing thelow frequency difference of the received radiations with the lowfrequency differences of the original transmitted radiations to measurethe phase difference of the received radiation and thereby the distancetraveled by the original and return radiations, a data processing unit(DPU), electronic means to transmit data digitally to said DPU from themeasurements of the angular position of said weapon, the measurements ofthe angular position of said television camera and the position of saidimage on said image surface, and data from said range measuringapparatus, means to activate said DPU operated by the firing mechanismof said weapon, and exhibition means controlled by said DPU to exhibitthe quantitative difference between the correct line of aim and the lineof aim of said weapon.
 7. In a system as claimed in claim 6, in whichsaid radio apparatus at said target transmits high frequency radiationswhich differ in frequency from the high frequency radiations transmittedby said first radio apparatus.
 8. In a system as claimed in claim 6, inwhich a light source is positioned on said target, and forms an image onthe image surface of said television camera.
 9. In a system as claimedin claim 6, in which the measuring apparatus to measure the elevationangle of said weapon is carried by the weapon supporting structure, andthe azimuth angle measuring apparatus includes a ground location pointspaced from said supporting structure to provide a measurement of theazimuth angle by reference to a fixed ground position.
 10. In a systemaccording to claim 9, in which said DPU actuates said exhibition meansto exhibit the differences in the values of the angles of elevation andazimuth, respectively, between the correct line of aim and the line ofaim of said weapon.